1. Field of the Invention
The invention relates to a working machine, such as an industrial truck, having working hydraulics, a hydraulic steering device, and a spring-loaded brake. The brake has a braking position and a release position and can be acted upon by means of a brake-release pressure, which is passed in a brake line, so as to be brought into the release position. A hydraulic pump is provided for the supply to the working hydraulics and the steering device and for producing the brake-release pressure of the spring-loaded brake.
2. Technical Considerations
DE 197 52 022 A1, herein incorporated by reference, discloses a generic working machine in the form of an industrial truck. A hydraulic pump is provided for the supply of hydraulic fluid to the hydraulic steering device, for the supply to the working hydraulics, and for producing a brake-release pressure that acts upon a spring-loaded brake forming a parking brake device so as to bring it into the release position.
In DE 197 52 022 A1, the brake line carrying the brake-release pressure is connected to a delivery branch line, which leads to the working hydraulics and is connected to the pump. In order to release the spring-loaded brake and, thus, to produce a brake-release pressure arising in the brake line, an additional valve is required, which acts upon a pressure balance, which controls the connection between the delivery branch line of the working hydraulics and a tank, so as to bring it into a blocking position. When producing the brake-release pressure passed in the brake line and, thus, when releasing the spring-loaded brake, the pressure balance is acted upon so as to be brought into the blocking position. As a result of which, the load-independent control of the consumers of the working hydraulics is brought out of operation given a simultaneous actuation of the working hydraulics, and a minimum delivery pressure arises in the delivery branch line of the working hydraulics. This minimum delivery pressure corresponds to the brake-release pressure, which results in a high energy requirement.
In addition, generic working machines are known in which the brake line is connected to the delivery branch line of the working hydraulics. The brake line is connected to a control face, which acts in the direction of the blocking position, of a pressure balance, which controls the connection between the delivery branch line of the working hydraulics and a tank. The control face, which acts in the direction of the blocking position, of the pressure balance is relieved of load by means of a safety valve in a safety position of the safety valve to the tank. In an operating position of the safety valve, the connection of the control face to the tank is blocked. With such a working machine, the safety valve is acted upon so as to be brought into the operating position for the purpose of releasing the spring-loaded brake and, thus, for the purpose of producing the brake-release pressure. Owing to the brake-release pressure arising at the control face, which acts in the direction of the blocking position, of the pressure balance, the delivery pressure produced by the pump is determined by the brake-release pressure. As a result of which, given a simultaneous actuation of the working hydraulics, a load-independent control of the consumers of the working hydraulics is not made possible in the case of a load pressure of the consumer of the working hydraulics, which falls below the brake-release pressure. In addition, if only the working hydraulics are actuated by the pressure balance being acted upon by the brake-release pressure in the delivery branch line of the working hydraulics, a minimum delivery pressure arises, which corresponds to the brake-release pressure, which results in a high energy consumption. Owing to the fact that the safety valve is acted upon so as to be brought into the operating position for the purpose of producing a brake-release pressure, in addition the safety function is brought out of operation, it being possible for an uncontrolled and arbitrary movement of the consumer of the working hydraulics to take place in the event of a control slide of a control valve, which controls a consumer of the working hydraulics, becoming stuck.